Conventionally, a method of recording an image and arbitrary additional information on a print medium such as a single sheet surface or the like has been proposed. For example, according to Japanese Patent Laid-Open No. 2000-348040, additional information is converted into a two-dimensional dot code, which is printed on the same sheet surface as the image. FIG. 37 is a view for explaining an image and additional information, which are printed on a sheet surface using the prior art. In FIG. 37, an image 3701 and two-dimensional dot code 3702 are printed on a single sheet surface 3703. Conventionally, a region of the two-dimensional dot code 3702 is scanned by an optical scanner such as an image scanner or the like to restore original additional information.
With this method, audio information, large-size text information, and the like, which cannot be conventionally transmitted by only a sheet surface, can be transmitted via a print medium, i.e., the sheet surface.
However, the above prior art suffers the following problems. In the conventional method, additional information must be restored by analyzing an image dot pattern obtained by reading only the region of the two-dimensional dot code 3702 in FIG. 37 using the optical scanner such as an image scanner or the like. For example, if the restored additional information is text data, the restored text data alone is displayed by a display method shown in FIG. 38. FIG. 38 shows an example of a display method of text data or the like restored using the prior art.
For example, assume that information contained in the two-dimensional dot code 3702 in FIG. 37 is closely related to the image 3701, i.e., it is a greeting message from a person who appears in the image 3701, or is a detailed comment for a product as an object. At this time, if text data alone is displayed, as shown in FIG. 38, the user who observed that data cannot feel sense of identity between the image and additional information.
In the above example, the two-dimensional dot code 3702 is printed on a region different from the image. Also, a technique for embedding additional information in an image is known. Such technique is generally called digital watermarking, and is standardized. With this technique, additional information of an author name, license, or the like is multiplexed on image information of a photo, picture, or the like to be visibly unrecognizable, and such information is distributed via a network such as the Internet or the like.
As another application field, in order to prevent paper money, stamps, securities, and the like from being counterfeited with the advent of high-quality image output apparatuses such as copying machines, printers, and the like, a technique for embedding additional information in an image to specify an output apparatus and its model number from an image output on a paper sheet is known.
For example, U.S. Pat. No. 5,652,626 has proposed a technique for multiplexing information by embedding additional information in a high-frequency range of color difference and saturation components with low visibility.
The assignee of the present applicant has already proposed a method of embedding many codes of additional information by artificially generating combinations of quantization values which cannot be generated by normal pseudo halftoning, and generating regularity in texture produced by error diffusion upon executing the pseudo halftoning based on error diffusion. With this method, since the texture pattern slightly changes microscopically, nearly no deterioration of image quality is observed. If a method of changing a quantization threshold value of error diffusion is used, since the density value of dot area modulation can be visibly preserved, different types of signals can be easily multiplexed.
FIGS. 1A and 1B are block diagrams showing the arrangement of an image processing system proposed by the present applicant. In FIGS. 1A and 1B, reference numerals 100 and 104 denote input terminals. Multi-tone image information is input from the input terminal 100, and additional information to be embedded in the image information is input from the input terminal 104. As the additional information, various kinds of information different from the image information may be used. The additional information undergoes an encoding process for error correction by an error correction encoder 103. As the error correction code, various kinds of codes such as a BCH code, Reed-Solomon code, and the like may be used. Multiplex information obtained as a result of error correction encoding is input to an additional information multiplexer 101. This additional information multiplexer 101 is a device for visibly unrecognizably embedding additional information in image information. The additional information multiplexer multiplexes the additional information, and also quantizes the input multi-tone image information. Reference numeral 102 denotes a printer which outputs information generated by the additional information multiplexer via a printer engine. As the printer, a printer which implements tone expression using pseudo halftoning such as an ink-jet printer, laser printer, or the like may be used.
Information on an output print is scanned using a scanner 105, and an additional information demultiplexer 106 analyzes the regularity of texture generated in the print process, thereby demultiplexing the additional information embedded in the print. The demultiplexed additional information undergoes an error correction decoding process by an error correction decoder 107, and is then output from an output terminal 108.
With the aforementioned method, large-size information can be surely multiplexed in image information without deteriorating the quality of that image information.
However, an image region printed on a sheet is merely considered as a recording medium, and has the same purpose as recording media such as a floppy disk, CD-ROM, and the like. That is, the added information itself is handled as sole information, and generates no new effect in combination with an image which serves as an information multiplexing region.